This invention relates to a process for the removal of hydrogen sulfide from gas mixtures by scrubbing with an aqueous alkaline scrubbing solution containing five-valent vanadium (vanadate) as the oxidizing agent. The sulfide of the hydrogen sulfide is converted into higher oxidation states with the simultaneous reduction of the five-valent vanadium to four-valent vanadium. The scrubbing solution is preferably subsequently regenerated for reuse in a downstream oxidizer by treatment of an oxygen-containing gas for the reoxidation of the four-valent vanadium.
A process of this type is described, for example, in British Patent Specification No. 1,488,659. According to this process, the gas to be cleaned is scrubbed with an aqueous alkaline solution, such as a sodium carbonate solution having a pH between 8 and 9, this solution containing a soluble salt, such as the sodium salt of anthraquinonedisulfonic acid, and a metal vanadate, the vanadium being in the five-valent oxidation state. The absorbed hydrogen sulfide dissociates in the solution with the formation of HS.sup.- ions which reduce the vanadium to the four-valent oxidation states, elementary sulfur being liberated. The reduced vanadium can be reoxidized by an oxidation reaction with an oxygen-containing gas in the presence of the anthraquinonedisulfonic acid.
It has been demonstrated that, at low pH values, for example below 9.5, in the scrubbing solution, a difficulty arises insofar as the rate of reaction of reoxidation of vanadium is decreased. In such cases, it is frequently not economically feasible to achieve complete reoxidation of vanadium. Thus only a part of the vanadium dissolved in the scrubbing solution is available in the five-valent state for subsequent absorption of the scrubbing solution with hydrogen sulfide.